A CRT (cathode ray tube) is one of display devices which are generally used in a monitor of a measuring instrument, an information terminal etc. as well as a TV, but it cannot actively corresponds to the demand of making an electronic appliance small and light due to the CRT's own weight and size.
Accordingly, the display devices, which are expected to replace the CRT which has a certain limit in weight and size when various electronic appliances are on the trend of being made small and light, include a liquid crystal display LCD using an electric field optical effect, a plasma display panel PDP using a gas discharge, an organic light emitting diode OLED using an field effect luminous effect. Among them, the liquid crystal display device has actively been researched.
In order to replace the CRT, the liquid crystal display device having advantages such as compact size, light weight and low power consumption has recently been developed to act sufficiently as a flat panel display and is used in a monitor of a desktop computer and a large-size display device as well as a monitor of a notebook computer, thus the demand for the liquid crystal display device is continuously increasing.
The liquid crystal display device like this generally includes a liquid crystal module LCM, a drive circuit part for driving the liquid crystal module, and a case. And, the liquid crystal module includes a liquid crystal display panel where liquid crystal cells are arranged in amatrix shape, and a backlight unit which irradiates light to the liquid crystal display panel.
The liquid crystal display device not being a self-luminous display device needs a separate light source like a backlight unit. And the liquid crystal display device is divided into an edge type and a direct type in accordance with a location where the light source is installed.
The light source of the backlight unit can be a cold cathode fluorescent lamp CCFL, a hot cathode fluorescent lamp HCFL, an external electrode fluorescent lamp EEFL, a light emitting diode LED, etc, and the CCFL or the LED are mainly used among them.
Additionally, in case of the liquid crystal display device which uses the CCFL or LED as the light source device, there is generated a problem in that brightness is decreased in accordance with a temperature as shown in FIGS. 1 and 2.
FIG. 1 represents a brightness change of a CCFL in accordance with a temperature, and FIG. 2 represents a brightness change of an LED in accordance with a temperature.
Referring to FIGS. 1 and 2, it is known that the brightness is remarkably deteriorated when a temperature is high or low in the CCFL and when a temperature is high in the LED.
Further, the temperature of the light source has a close relationship with an operation life span to be directly connected to the reliability of the product as well as being a problem of the brightness deterioration.